For externally described files, only the fields specified are placed in the output record. *ALL can be specified to include all the fields in the record. If *ALL is specified, no other field description lines can be specified for that record. In particular, you cannot specify a B (blank after) in position 45.
For an update record, only those fields specified in the output field specifications and meeting the conditions specified by the output indicators are placed in the output record to be rewritten. The values that were read are used to rewrite all other fields.
For the creation of a new record (ADD specified in positions 18-20), the fields specified are placed in the output record. Those fields not specified or not meeting the conditions specified by the output indicators are written as zeros or blanks, depending on the data format specified in the external description.